1. Field of the Invention
The present invention relates to narrow band communication vehicle-mounted apparatus for use in advanced road traffic systems and the like, and in particular, to a narrow band communication vehicle-mounted apparatus that can perform communication in which there are normally no discrepancies with on-road systems.
2. Description of the Related Art
A system which is beneficial for drivers and on-road systems administrators is brought about by performing communication, using narrow band communication (DSRC Dedicated Short Range Communication), between an on-road device provided on a road and vehicle-mounted apparatus provided in an automotive vehicle and exchanging various types of data.
Regarding the narrow band communication vehicle-mounted apparatus used in this system, to say nothing of a conventional narrow band communication vehicle-mounted apparatus which does not have nonvolatile memory, even when the apparatus does have memory temporarily, communication registration identification data is not saved. For example, in the case where the narrow band communication vehicle-mounted apparatus goes down while the vehicle is traveling, when the device starts up it re-performs narrow band communication using communication registration identification data generated when the power source was started or when communication was commenced.
On the other hand, in conventional narrow band communication vehicle-mounted apparatus having nonvolatile memory, an identification number of the on-road device is also stored in the nonvolatile memory and classificatory discrepancies of on-road device are determined from an identification number of the on-road device during communication, and it is determined whether communication registration identification data is newly generated or saved communication registration identification data is continued and used. For example, in a case where the same type of on-road device is present when the vehicle-mounted apparatus starts up as when it went down, the saved communication registration identification data is continued and used.
Furthermore, in another conventional narrow band communication vehicle-mounted apparatus, to say nothing of conventional narrow band communication vehicle-mounted apparatus which does not have nonvolatile memory, even when the apparatus does have memory temporarily, a communication frequency is not stored. When the apparatus is started, a procedure which is predetermined by a control program and the like in the apparatus is followed and a new frequency is selected. When this new frequency is selected, generally, whether or not communication is possible at a first candidate frequency is determined. If it is possible, communication is performed at this frequency, if it is not possible, a second candidate frequency and so on are checked and a frequency at which communication is possible is selected. That is, for example, first whether or not communication is possible at a preset lowest frequency is checked and then sequentially higher frequencies are checked.
In narrow band communication with such a system, (radio) waves are reflected by wall and pillars and the like included in the system and such wave reflection causes waves to leak into an adjacent communication area of the on-road device. Adjacent on-road devices have different radio frequencies so that communication does not become crossed. However, when there is this type of wave leakage, it may become possible for the vehicle-mounted apparatus to communicate with both adjacent on-road devices.
FIG. 5 is a diagram explaining this condition. In FIG. 5, in the exit-side on-road system, waves transmitted from an on-road antenna are reflected at side walls of the exit-side on-road system and leak into the entrance-side communication area. Thus, a portion of communication for the exit-side is present in the entrance-side communication area.
In conventional narrow band communication vehicle-mounted apparatuses, when, in the communication area of the on-road device performing transmission (called the normal-side: concretely, the entrance-side in FIG. 5), the vehicle-mounted device starts up after having gone down due to engine stall and the like, the vehicle-mounted device may use newly generated communication registration identification data to communicate with a different on-road device than before it went down (the wave reflection-side, herein below called the leakage-side: concretely, the exit-side in FIG. 5).
In such an event, since, in the normal-side on-road device which performs communication after the leakage-side on-road device has finished communication, the communication registration identification data of the narrow band communication vehicle-mounted apparatus differ from before the vehicle-mounted apparatus went down, the on-road device recognizes it as a new vehicle-mounted apparatus and restarts communication. Hence, there is a problem in that when the vehicle-mounted apparatus starts up after having gone down, it may be recognized as a different vehicle-mounted apparatus (a different automotive vehicle) at normal-side on-road device.
In storing the above communication registration identification data and identification number, a similar problem also occurs in the vehicle-mounted apparatus whether, taking into consideration the identification number of the on-road device during communication, it determines that communication registration identification data should be newly generated or saved data should be continued and used. For example, as shown is FIG. 5, when adjacent on-road systems have different functions (for example, an exit and an entrance for highway toll collection), in the case where, while communicating with the normal-side on-road equipment or having started up after having gone down after communication, the narrow band communication vehicle-mounted apparatus communicates with the leakage-side on-road device, communication registration identification data is newly generated for the normal operation of “end of entrance, exit”, and there is a problem in that the normal-side on-road equipment will recognize the vehicle-mounted apparatus as being a different apparatus. Also, when observing the same thing from the perspective of the leakage-side on-road system, there is a problem in that a narrow band communication vehicle-mounted apparatus is present in an area that it should not be for normal communication and a processing error occurs.
In a case where there is wave leakage to the communication area of an adjacent on-road device due to wave reflection such as above, communication becomes possible with both on-road devices in conventional narrow band communication vehicle-mounted apparatuses. Although radio frequencies at adjacent on-road antennas differ, in this condition, communication with both on-road devices becomes possible (FIG. 5). Here, when, in the communication area of the on-road device performing transmission, the vehicle-mounted device restarts after having gone down due to engine stall and the like, a microcomputer control program does not select a radio frequency by a predetermined procedure and communication may occur with a different on road device than before the apparatus went down. Thus, there is a problem in that, from the perspective of the leakage-side on-road system, a narrow band communication vehicle-mounted apparatus is present in an area that it should not be for normal communication and a processing error occurs. Also, since time is required for communication with the leakage-side on-road system which is a different system than before the vehicle-mounted apparatus went down, there is a problem in that there is a delay before communication is reopened with the normal-side device with which the vehicle-mounted apparatus communicated before it went down and communications processing of a (data) string is not finished in the communication area.